The present invention relates to backscatter communication systems, interrogators, methods of communicating in a backscatter system, and backscatter communication methods.
Electronic identification systems typically comprise two devices which are configured to communicate with one another. Preferred configurations of the electronic identification systems are operable to provide such communications via a wireless medium.
One such configuration is described in U.S. patent application Ser. No. 08/705,043, filed Aug. 29, 1996, assigned to the assignee of the present application, and incorporated herein by reference. This application discloses the use of a radio frequency (RF) communication system including communication devices. The disclosed communication devices include an interrogator and a remote transponder, such as a tag or card.
Such communication systems can be used in various applications such as identification applications. The interrogator is configured to output a polling or interrogation signal which may comprise a radio frequency signal including a predefined code. The remote transponders of such a communication system are operable to transmit an identification signal responsive to receiving an appropriate polling or interrogation signal.
More specifically, the appropriate transponders are configured to recognize the predefined code. The transponders receiving the code subsequently output a particular identification signal which is associated with the transmitting transponder. Following transmission of the polling signal, the interrogator is configured to receive the identification signals enabling detection of the presence of corresponding transponders.
Such communication systems are useable in identification applications such as inventory or other object monitoring. For example, a remote identification device is attached to an object of interest. Responsive to receiving the appropriate polling signal, the identification device is equipped to output an identification signal. Generating the identification signal identifies the presence or location of the identification device and the article or object attached thereto.
Some conventional electronic identification systems utilize backscatter communication techniques. More specifically, the interrogator outputs a polling signal followed by a continuous wave (CW) signal. The remote communication devices are configured to modulate the continuous wave signal in backscatter communication configurations. This modulation typically includes selective reflection of the continuous wave signal. The reflected continuous wave signal includes the reply message from the remote devices which is demodulated by the interrogator.
Certain drawbacks have been identified with the use of backscatter communication techniques. For example, the transmission of the continuous wave signal using the interrogator can desensitize the receiver of the interrogator during reception thereby of reply signals from associated remote devices. In particular, some of the continuous wave signal tends to bleed through to the received reply messages. Such results in degradation of wireless communications.
There exists a need to provide a system which provides improved wireless communications without the drawbacks associated with conventional devices.
The present invention includes backscatter communication systems, interrogators, methods of communicating in a backscatter system, and backscatter communication methods.
One aspect of the present invention provides a method of reducing power within a modulated return link continuous wave signal of a coherent backscatter communication system including an interrogator and at least one remote communication device. Exemplary remote communication devices include remote intelligent communication (RIC) devices and radio frequency identification devices (RFID) of electronic identification systems.
The interrogator preferably comprises a coherent interrogator configured to provide backscatter communications. More specifically, the interrogator is configured to output a forward link communication and a wireless continuous wave signal using a transmitter. The interrogator is also configured to output a local continuous wave signal to a receiver of the interrogator following transmission of the forward link communication. Provision of the local signal enables coherent operation of the interrogator. The interrogator is operable to receive return link communications from at least one remote communication device responsive to transmission of the forward link wireless communication.
In some embodiments, the interrogator includes a receiver operable to reduce the amplitude of a carrier signal of the return link communication. For backscatter communications, the remote communication device is configured to modulate the continuous wave signal providing a carrier component and side band components. The receiver of the interrogator is preferably configured to reduce the amplitude of the carrier component while maintaining the amplitudes of the side band components.
A communication method according to one aspect of the present invention provides reduction of the amplitude of the carrier component of the modulated continuous wave signal. This method includes the steps of matching the amplitude of a local continuous wave signal with an amplitude of a modulated continuous wave signal; adjusting the phase of the local continuous wave signal following the matching; and summing the local continuous wave signal and the modulated continuous wave signal following the adjusting. The adjusting the phase preferably comprises searching for a phase adjustment of the local continuous wave signal which provides maximum reduction of the amplitude of the modulated continuous wave signal at the frequency of the wireless continuous wave signal.